What Is A Tree Flare: Should I Be Able To See A Tree’s Roots

Green Grass Growing Over Tree Root Flare
tree flare
(Image credit: Gardening Know How, via Nikki Tilley)

You may worry about getting thicker around the middle, but the same rules don’t apply to your trees. In the wild, tree trunks flare out just above the soil line, indicating where the root system begins. If the flare is covered with soil, the roots cannot get the oxygen the tree needs. Exactly what is a tree flare? Is root flare important? Read on for root flare information.

What is a Tree Flare?

If you aren’t experienced with tree planting, you may be curious about tree flares. A tree flare, also called root flare, is the broadening of a tree’s trunk just above the soil line. Is root flare important to a tree’s health? It is very important as an indication of where the trunk ends and the root system begins. Most roots are found in the 12 inches (30.5 cm.) of soil just below the tree flare. They stay close to the top of the soil in order to complete the oxygen exchange, essential for the tree’s survival.

Root Flare Information

When you are planting a tree in your backyard, root flare depth is of prime importance. If you plant the tree deep in the ground so that the root flare is covered with soil, the roots cannot access the oxygen the tree requires. The key to determining root flare depth when you are planting is to make a point of finding the root flare before putting the tree in the ground. Even in container-grown or ball-and-burlap trees, the tree flare can be covered by soil. Carefully remove the soil around the tree’s roots until you locate the tree flare. Dig a planting hole sufficiently shallow so that when the tree is placed in it, the flare is fully visible above the soil line. If you are worried about disturbing the tree’s roots, dig a hole to the proper depth and place the entire root ball in it. Then remove the excess soil until the root flare is fully exposed. Only then backfill the hole up to the base of the root flare. You may get the tree in the ground and wonder if you’ve done it wrong. Many gardeners ask: should I be able to see a tree’s roots? It doesn’t hurt a tree to have some of its top roots exposed. But you can protect them by covering them with a layer of mulch, right up to the base of the root flare. Remember that the root flare is actually part of the trunk, not the roots. That means it will rot if consistently exposed to moisture, as it will be under the soil. The tissue that rots is the phloem, responsible for the distribution of energy manufactured in the leaves. If phloem deteriorates, the tree is no longer able to use food energy for growth. Adjusting for proper root flare depth is essential to maintaining a healthy tree.

Teo Spengler

Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.